We propose to examine structures and properties of classical and nonclassical nucleic acid bases using theoretical methods. One specific aim of this research is to study molecular structures of the above compounds by ab initio quantum mechanical calculations. We shall study classical purine nucleic acid bases, classical pyrimidine nucleic acid bases as well as non-classical systems which might increase catalytic role of RNA and DNA molecules and the fidelity of replications. We shall predict relative energies of the "normal" and "rare" tautomers of classical and nonclassical species and relate the probability of spontaneous mutations to the equilibrium constant of the transition between the normal and rare tautomers. Different derivatives of the classical NABs will be examined to gain an understanding of how selected substituents could modify the probability of spontaneous mutations of the parent molecules. We shall assist experimental studies on the title species by theoretical molecular geometries, dipole moments, rotational constants and vibrational frequencies and intensities. We shall expose underrepresented minorities to the theory and practice of the quantum chemical methods. The development of the computer and supercomputer literacy as well as the oral and written communicative skills of students will be a major thrust of this research project.